Stroke is a deadly and debilitating disease striking 700,000 Americans each year. Nearly 75% of these strokes are ischemic or caused by blood clots which stop blood flow to areas of the brain resulting in brain cell death. Once a patient seeks medical care, the largest challenge to preventing stroke-related disability is rapidly achieving lysis of the clot that is blocking blood flow. The faster the blood supply can be restored to the oxygen starved portions of the brain the less disability suffered by the patient. Locally directed ultrasound energy can enhance blood clot lysis resulting in a faster return of blood flow to the ischemic brain tissues. The goal of this project is to demonstrate that ultrasound energy radiating from the end of a catheter can enhance the lysis of blood clots in the neurovascular system for the treatment of stroke. The specific aims of this Phase I project are to: 1. Downsize the current EKOS ultrasound catheter to a 3.5 French product. 2. Demonstrate the ability of small ultrasound transducers to lyse plasma clots in vitro. 3. Demonstrate the ability of the downsized ultrasound catheters to lyse blood clots in vivo. PROPOSED COMMERCIAL APPLICATIONS: Our product will be an ultrasound microcatheter which will be used in the treatment of stroke.